1. Field of the Invention
This invention relates to a method and apparatus for minimizing the electrostatic charges developed in transient flowing fluids, such as hydrocarbon fuels, using the corona discharge method.
The accumulation of electrical charges in a moving fluid has long been a problem to the safe handling of flammable liquids. There are numerous instances where static charges have accumulated to levels high enough to cause a discharge of sufficient intensity that ignition of the flammable liquid resulted.
The most prevalent of the electrostatic induced accidents has been in connection with tank truck and storage vessel loading operations. The spark discharge in such instances occurs between the surface of the charged fluid in the tank or vessel and some component of the tank or vessel system such as reinforcing members, gauge markers, or the loading spout. This type of sparking is internal and can occur whether or not the tank or vessel is grounded to the loading pipe assembly.
A number of methods have been employed to reduce the safety hazards involved in handling flammable hydrocarbon fluids. Among them are: (a) relaxation tanks wherein the charge on the liquid is allowed to dissipate naturally, in the absence of air, before the liquid enters the receiving tank, (b) the use of a static dissipater additive to increase the conductivity of the liquid and thereby promote the rapid dissipation of charge, and (c) the static charge neutralizer, which employs pointed electrodes protruding from a plastic lining of a pipe into the flowing liquid to dissipate the charge by means of a lightning rod effect. Relaxation tanks are impractical where low-conductivity liquids must be moved at high flow rates since the size of the tank required to reduce the charge on the liquid to a safe level becomes prohibitively large. Although the static dissipater additive protects the product during all phases of handling, it does have the disadvantage of interfering with the water separator characteristics in the instances where it's being used on a fuel. The static charge neutralizer employs a continuous corona inside the moving liquid to neutralize the charge.
In many liquid-hydrocarbon-handling systems, the filter is possibly the greatest single cause of static electricity buildup in such systems. This is mainly due to its large surface area which allows great amounts of charge separation at the filter surface and liquid interface. This mechanism results in the generation of high electrostatic charges. Also, there is a tendency to locate filters close to the loading point. As a consequence, when the liquid is discharged into a tank or vessel it is in a highly charged and dangerous condition.
2. Description of the Prior Art
Filter cartridges containing tight filter media, by nature generate electrostatic charges, which flow with the fuel as it exits the filter. A 2″ OD outside-in flow filter/monitor, used routinely as the last filtration step before fuel is loaded onto an aircraft, generates the highest charging due to its construction and flow path.
For many years, anti-static additives have been used in jet fuel to reduce electrostatic charging. This has been the single most important factor leading to lower fire hazards for aircraft. This additive works by increasing the electrical conductivity of the fuel, allowing static charges to dissipate by flowing through the fuel itself to ground. This process typically occurs in a few seconds. However, this additive can act as a pro-static agent on refueling vehicles containing these filter/monitors, increasing electrostatic charging. Charging is much higher on vehicles and spark discharges occur routinely inside the pressure vessels containing these filter/monitors. If air is present inside these pressure vessels while electrostatic spark discharges occur, the risk of fire and explosion is high.
There is a real need to reduce this charging in current systems. These inventors have developed a device, which attaches to the end of the monitor cartridge (patent pending). This is not the preferred solution. It is most advantageous to build in this static charge reduction into the present monitor cartridge.
Previous patents (e.g. U.S. Pat No. 3,619,718 by Leonard) address charge reduction methods which utilize the triboelectric effect of differing materials. Materials such as glass charge positively, while materials such as polyester charge negatively. Using materials, which charge with opposite polarity, the charge could be neutralized inside the cartridge. However, filter media vary in fiber diameter, density, surface coatings, etc. which makes this approach very difficult in practice. In addition, industry qualification specifications require these filter/monitors to perform a variety of functions, which limit the opportunity to utilize the triboelectric effect in filter/monitor design.
It is an object of the present invention to produce an apparatus which will minimize the safety hazard caused by the build-up of static electricity in moving liquids.
Another object of the invention is to produce an apparatus which will prevent the build-up of electrostatic charges to levels high enough to cause an ignition spark in liquid hydrocarbon handling systems.
Still a further object of the invention is to produce an apparatus to effect a neutralization of accumulated electrostatic charge upon a flowing hydrocarbon liquid.
A further object of the invention is to produce a fuel filter/monitor wherein the inner support area is made to immediately neutralize static charges in a transient hydrocarbon fluid passing therethrough.
A further object of the invention is to produce a fuel filter/monitor wherein the inner support area includes branched conductive paths where the charge can be neutralized.
Still another object of the invention is to produce a fuel filter/monitor capable of neutralizing the filter generated electrostatic charge in the transient hydrocarbon fluid using the corona discharge method.